Export of phosphorus and nitrogen from agricultural river basins in Korea

Abstract 2011: The effectiveness of best management practices in improving quality of runoff from agricultural land areas has been reported, based primarily on results from plot- and field-scale studies. There is limited information available at watershed scales, particularly with dominant agricultural land use. The objective of this study was to determine whether a program of Best Management Practice (BMP) implementation in an agricultural watershed of northwestern Kangwon Province was effective in reducing storm streamflow concentrations of total phosphorus (TP) and total suspended solids (TSS). Furthermore, we determined the removal efficiency for three proposed BMPs (a sand settling basin, debris barriers, and crop manipulation). Water quality of the small stream in the watershed was monitored from May 2009 to November 2010. The settling basin showed 80% removal efficiency of TSS. But there was no removal efficiency of TSS with debris barriers. The export coefficient from peach orchards was very low compared with other crops. Significant decreases (20 times and 8 times, respectively) in the event mean concentrations (EMC) of TP and TSS were found in 2010 when the BMPs were implemented. Nevertheless, we are not able to conclude whether the decreases in TP and TSS are attributed directly to BMP implementation, since the rain intensity was not the same in 2009 and 2010. Further study is required.

Keywords: Best management practices, water quality, nonpoint source pollution, event mean concentration

Abstract 2013: While BOD (biochemical oxygen demand) has decreased in the Han River, COD (chemical oxygen demand) has increased in the last 20 years. The cause is release of non-biodegradable organic matter from agriculture and forests to the river system. Recently, the Korean EPA has tried to change the criteria for evaluating water quality in terms of organic matter content from BOD and COD to TOC (total organic carbon). But not many TOC data are available upon which to base the criteria. Therefore, we began studies in two different land use areas, and estimated export coefficients for organic matter. The study site is a bowl-shaped mountainous catchment in northern part in South Korea, Haean Catchment. About 50% of land-use was agricultural land, and its mean slope range 5 to 10 degrees. We investigated 22 rain events in four  agricultural streams, and in a forest stream from 2009 to 2012. BOD, COD, DOC, POC increased greatly in agricultural streams during storm events. In the forest stream, COD and DOC increased, but BOD and POC did not at the beginning of the rain event. It means that much non-biodegradable organic matter is exported from forests as DOC at low flow rates. While POC remained lower than DOC during low rainfall intensity, COD and POC showed larger increases in the forest stream during storm events which have high rainfall intensity. EMC of BOD and COD in the forest stream were lower than in agricultural streams, but TOC was similar with other agricultural streams. It means that TOC as an indicator of organic matter is more suitable than BOD and COD in forest streams. TOC export coefficients in the agricultural catchment ranged from 20 to 150 kg/ha/yr which are about 30 times higher than other studies because of croplands cultivated on steep mountain slopes. TOC export coefficients in the forested catchment ranged from  2.3 to 7.6 kg/ha/yr and are similar to other studies.

Keywords: water quality, land use, organic carbon, export coefficients, event mean concentration

DFG funding ID 88758029

Poster Workshop Ecosystem Change and Society, Bayreuth, January 2013